2-Octanone, mass spectrum

The peak at m/e = 58 in the mass spectrum of 2-octanone is due to the fragment ion that results from this rearrangement. 

The results of both a-cleavage and McLafferty rearrangement can be seen in the mass spectrum of 2-octanone (Figure 14.11). 

Mass spectrum of 2-octanone. Ions at m/z 43 and 113 result from a-cleavage.The ion at m/z 58 results from McLaffer rearrangement. 

When the carbonyl group of a ketone has attached to it at least one alkyl group that is three or more carbon atoms in length, a McLafferty rearrangement is possible. The peak at m z = 58 in the mass spectrum of 2-octanone is due to the fragment ion that results from this rearrangement. 

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